Recently, a vehicle-mounted motor and an electronic control unit for driving the motor are increasing. On the other hand, in order to extend vehicle interior space, the space for arranging the motor and the electronic control unit is decreased. Therefore, size reduction of the motor and the electronic control unit is desired.
Japanese Patent No. 2684893 B2 discloses a hybrid integrated circuit, a size of which is reduced by arranging transistors on both surfaces of a circuit board.
For example, an electronic control unit for driving a motor of an electronic power steering system (hereinafter referred to as EPS) that assists steering by a driver is energized by large current, and thus, its heating value becomes large. The electronic control unit for the EPS is placed in an engine room or a narrow space behind an instrument panel. If the electronic control unit is configured as described in Japanese Patent No. 2684893 B2, thermal interference is generated between electronic components (hereinafter referred to as heat generating components) that generate heat with the energization. Therefore, it may become difficult to apply large current.